11-08-2011 07:49 AM - edited 03-04-2019 02:12 PM
I'm trying to write a QoS policy for a branch router using CBWFQ to utilize the priority queue for voice. I already know how much bandwidth I need for each traffic class. So I am trying to calculate the percentage of BW required based on how much BW I need. I am having trouble with the percentage of traffic I am reserving matching up with the actual amount of BW I am trying to reserve.
From what I have read, when using the remaining bandwidth command, the percentage of bandwidth is calculated by the following logic: remaining BW = interface total BW - (priority queue + .25 * interface BW). The percentage allocated using the remaining bandwidth command is calculated using the remaining BW not the interface total BW.
If the above is true, then why aren't my numbers matching up with the BW in the show policy-map command? I have configured an Ethernet interface for 1536 BW.
1536 * .25 = 384 (25% non-reservable)
1536 * .21 = 322.56 (21% for priority queue)
384 + 322.56 = 706.56 (25% of int BW + 21% for priority queue)
1536 - 706.56 = 829.44 (remaining available BW)
I know I want to allocate 77kbps for voice signaling, which is 9% of the remaining BW. 77 / 829.44 = .0928. However, the show policy-map interface command shows a different amount of BW reserved for 9%. It shows 109 kbps. I believe it gets 109 kpbs by calculating the remaining BW from the interface BW - priority queue, not interface bandwidth -(non-reservable BW + priority queue BW).
Does anyone know why I am seeing this?
----------LAB Configuration----------
class-map match-any VOICE-TRAFFIC
match access-group name VOICE-TRAFFIC
class-map match-all DEFAULT
match access-group name DEFAULT
class-map match-any MISSION-CRITICAL-APPS
match access-group name MISSION-CRITICAL-APPS
class-map match-any NETWORK-MANAGEMENT
match access-group name NETWORK-MANAGEMENT
class-map match-any IP-ROUTING
match access-group name IP-ROUTING
class-map match-any CALL-SIGNALING
match access-group name CALL-SIGNALING
!
!
policy-map STORES-QOS-POLICY
description DSW Store Router QoS Policy
class CALL-SIGNALING
set dscp cs3
bandwidth remaining percent 9
class IP-ROUTING
set dscp cs6
bandwidth remaining percent 15
class MISSION-CRITICAL-APPS
set dscp af31
bandwidth remaining percent 28
class NETWORK-MANAGEMENT
set dscp cs2
bandwidth remaining percent 15
class DEFAULT
set dscp default
class VOICE-TRAFFIC
set dscp ef
priority percent 21
interface FastEthernet0/1
bandwidth 1536
no ip address
shutdown
duplex auto
speed auto
!
service-policy output STORES-QOS-POLICY
yourname#show policy-map int fa0/1
FastEthernet0/1
Service-policy output: STORES-QOS-POLICY
queue stats for all priority classes:
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 0/0
Class-map: CALL-SIGNALING (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: access-group name CALL-SIGNALING
0 packets, 0 bytes
5 minute rate 0 bps
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 0/0
QoS Set
dscp cs3
Packets marked 0
bandwidth remaining 9% (109 kbps)
Class-map: IP-ROUTING (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: access-group name IP-ROUTING
0 packets, 0 bytes
5 minute rate 0 bps
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 0/0
QoS Set
dscp cs6
Packets marked 0
bandwidth remaining 15% (182 kbps)
Class-map: MISSION-CRITICAL-APPS (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: access-group name MISSION-CRITICAL-APPS
0 packets, 0 bytes
5 minute rate 0 bps
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 0/0
QoS Set
dscp af31
Packets marked 0
bandwidth remaining 28% (339 kbps)
Class-map: NETWORK-MANAGEMENT (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: access-group name NETWORK-MANAGEMENT
0 packets, 0 bytes
5 minute rate 0 bps
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 0/0
QoS Set
dscp cs2
Packets marked 0
bandwidth remaining 15% (182 kbps)
Class-map: DEFAULT (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: access-group name DEFAULT
QoS Set
dscp default
Packets marked 0
Class-map: VOICE-TRAFFIC (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: access-group name VOICE-TRAFFIC
0 packets, 0 bytes
5 minute rate 0 bps
QoS Set
dscp ef
Packets marked 0
Priority: 21% (322 kbps), burst bytes 8050, b/w exceed drops: 0
Class-map: class-default (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 0/0
11-08-2011 10:46 AM
Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
"1536 * .25 = 384 (25% non-reservable)"
a) that can be changed on the interface - has it been?
b) 25% default was changed in later IOS versions, what IOS version are you running?
Your remaining percent number all appear to be BW - priority %.
11-08-2011 11:35 AM
Answers to your questions:
a) I have not changed the max-reserved-bandwidth on the interface.
b) IOS 15.0(1)XA5
So, the new default is BW - priority %? What is the best practice for reserving BW then?
11-08-2011 04:12 PM
Disclaimer
The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
Liability Disclaimer
In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
Posting
If I remember correctly, CBWFQ's default bandwidth reservation changed with 12.4(20)T, so your 15.0 version should be using HQF QoS.
Actually it might be BW - all defined bandwidths other than remaining, but I'm unsure.
You might just use defined bandwidths or straight percentages.
11-08-2011 01:56 PM
You can consider using hqos with a shaper in the parent qos policy
Plz refer to the below document for more details
https://supportforums.cisco.com/docs/DOC-8373
Hope this helps
If helpful rate
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